Process for the manufacture of electrostatic condensers



Dec. 6, 1938. H s'rRAB ET AL PROCESS FOR THE MANUFACTURE OFELECTROSTATIC CONDENSEHS FiledApril 12, 1937 Patented Dec. 6, 1938UNITED STATES PATENT OFFICE 2,138,892 I xrltocnss roa rm; monomer; orELECTROSTATIC CONDENSEBS Application April 12, 1937, Serial No. 136,420

' I In Germany April 16, 1936 16 Claims. (Cl. 175-41) The presentinvention relates to electrostatic condensers.

Thedielectrics as for example paper or the like used for the manufactureof condensers, in particular of wound condensers sufier the disadvantagethat they do not have at every place of the total dielectric surface,the same resistance to break-down, but that minute holes or porousplaces occur, which very easily lead to the occurrence of break-down.

It is known that these bad places of the dielectric can be made lesstroublesome if very thin metal coatings are used, and, with the help ofover voltages an artificial break-down is obtained with so great acurrent that this burns out, the

metal coating round a break-down-spot. Hereby the metal coating is burntout in a region which is larger than the hole in the dielectric.

With this process on correct choice of the metal coating, the insulationof the dielectric can be considerably improved. However there is adanger that by 'the break-down process, small I conducting particles ofcarbon may beproduced in the insulating material, which may produce as aconsequence a certain even if small conductivity at the breakdown spots.

According to the invention this danger is overcome by not covering thedielectric with metal from the start at its weak or holed places andin'their immediate vicinity. If e. g. a metal foil is used as metalcoating of the condenser, those,

places may be cut or stamped out of the foil which come to lie on theweak places of. the dielectric on building up the condenser. Forascertaining the positions of the weak places of the dielectric air canbe blown from one side against the dielectric. From theamount of the airescaping through the dielectric, the positions of the weak places-may bedetermined. 40 The back side of the dielectric may also be painted witha coloured or fatty coating which penetrates at the weak places, and inthis manner the position of the weak places of the dielectrlc shows onthe front side. The weak places of the dielectric can in the simplestmanner be madeinto places not provided with a metallic coating, if thecoating of the condenser is obtained as a metal deposit directly on thedielectric for example by spraying, 5o spluttering orevaporation. If ondepomtion of the metals the weak places of the dielectric and theirimmediate vicinity are covered by stencils preferably circular in form,then the weak places remain free of metal.

.55 In the obtainment ofametaldeposit onaprogressing band of dielectric,as for example comes into question for the manufacture of woundcondensers, the use of stencils is unsuitable, since the stencils musttravel with the band. In this case it is preferable to apply to the weak'places I 5 of the dielectric and their immediate vicinity a covering ordeposition stopping material. After the metallization the coveringmaterial with the metal layer deposited thereon can be again removed.There can be used for this object, also 10 a covering material e. g. fator th like, on which the metal deposit obtained e. g. by spraying,adheres badly. After the precipitation the badly adhering metal layer onthe places covered may be wiped away.

-In many cases the same result can be obtained even more simply byapplying to the Weak places ofthe dielectric or their immediate vicinitybefore the deposition a substance which does not at all allow theproduction of a {metal deposit. 20 These properties are possessed ysubstances which evolve vapour on heating in vacuo. If such asubstanceis applied-to the weak places of the dielectric and the metal depositobtained in vacuo by cathode spluttering or purely thermal metalevaporation then no metal is deposited at these places since the vapoursproduced there act as a protective cushion. Precipitation preventingsubstances of this kind are for example aliphatic or aromatichydrocarbons and hydrocarbon-like substances such as for example, fatsoils, halogen derivatives of these hydrocarbons, alcohols (e. g.glycerin) resins, waxes, paraiiins and other organic substances. I

In order to obtain sharp definition of the 35 metallized and blankspaces, it is preferable to keep the laye'rsof covering or depositionpreventing substances as thin as possible. In this manner the edges ofthe coating are prevented from running. This danger, of the edgesrunning 0 is particularly great if any time elapses between theapplication of the covering or deposition preventing substances and theproduction of the metal coating. For this reason it is preferable toapply the coating or deposition preventing substances, directly beforethe metalllzation, and also in the same vessel, in whichthe-metallization There is another reason for applying the coatingsubstances very thinly. Long bands of di- 5 electric e. g. whole rollsof paper have mainly to be metallized. If it is wished to apply to theweak places of the dielectric coating or deposition preventingsubstances, and'to roll up the long dielectric band again before themetallizatlon, then there exists the danger that the coating materialswill leave behind traces of themselves on the neighbouring windings ofthe roll, and places free of metal will be caused in the subsequentmetallizing where these are not desired. Therefore those cases in whichoil or fats are used as deposition preventing layers e. g. in metalevaporation in vacuo they must only be applied very thinly.

In order completely to prevent this eiIect on the neighbouring windingof a roll the coating or deposition preventing substances are not onlyapplied very thinly, but also a substance is used which is solid or atleast semi-solid at normal temperatures.

In ordernot to affect the neighbouring windings, an additional paperstrip which prevents direct contact between the front and back sides ofthe single windings can also be wound with the treated bands.

The application of the coating or deposition preventing substance to theweak places of the dielectric can be very much simplified by not firstinvestigating where the weak spots in the dielectric are, but byapplying coating material in a liquid or semiliquid condition directlyto the rear side of the dielectric in a similar way to what wasdescribed above for the detection of the weak spots, in such a way thatthey pass through the weak places in the dielectric and spread out overa small range (about 1 to 5 mm. in diameter) around the weak spots. Ifnecessary the substance applied on the back side must be kept liquiduntil it has penetrated to the necessary degree through the dielectricby the use of high temperatures.

If for example fat has been applied to the back side of a paper bandtill it passes through the paper at the porous places, and spreads outfor a certain distance on the front side of the paper band, and if thefront side of this penetrated paper band is subjected in a vacuum vesselto a metal vapour then the weak places of the paper, protected by thefat, remain metal free. If the fat applying and evaporating places arearranged the one immediately behind the other and the nature of thedeposition preventing material, and the temperatures between applicationof fat and evaporating places are chosen so that this substance spreadsas easily and rapidly as possible then the whole process may be carriedout in a single operation.

In Figs. 1 and 2, is shown an example of construction of a metallizedcondenser paper prepared in the manner described.

Figure I shows a view .on the metallized side of the paper.

Figure 2 shows a section along the line 2-2 of Fig. l with a highlyexaggerated view of the thicknesses.

In the figures a denotes a paper band, on which is applied a metal layer1), c are weak places in the paper. On the metallized side of the paperthe metal coating is absent for a small region d around the weak places0, j is a metal free edge of the paper. If a second paper band is usedin which the metal free edge is on the other side, then these two bandsmay be wound up together to a wound condenser. Whilst in normal woundcondensers'several paper layers must always be used mutually to coverthe weak places of the paper, the additional nonmetallized paper layersare in most cases not necessary in the condensers prepared according tothe invention.

If the metal coating b is made thinner than 2 thus for example equal to1a or 0.1; or less, there is obtained the advantage that the weak placesof the dielectric produced somewhat with time, in the normal operationof the condenser can cause no injury. If such a condenser breaks down ata weak spot, then its own energy suiilces to send a short circuitingcurrent through the break-down spot so that the metal coating vanisheson account of the local heating here produced, over a range which islarger than the break-down hole in the dielectric. After such abreak-down the condenser is again fully operative, and has insulateditself again automatically.

We declare, that what we claim is:

1. In a process for the manufacture of electrostatic condensers, thesteps which comprise depositing a metal coating on a dielectric andprotecting the weak places of the dielectric against the deposition ofmetal.

2. In a process for the manufacture of electrostatc condensers, thesteps which comprise applying to the weak spots of a dielectric asubstance which can be removed and which prevents the deposition ofmetal thereon, and depositing a metal coating on the dielectric.

3. In a process for the manufacture of electrostatic condensers, thesteps which comprise applying to the weak spots of a dielectric asubstance to which the subsequent metal coating adheres badly,depositing a metal coating on the dielectric, and removing the badlyadhering portions of the coating.

4. In a process for the manufacture of electrostatic condensers, thesteps which comprise applying to the weak spots of a dielectric andtheir immediate vicinity a substance capable of pre-, venting thedeposition of metal, and depositing metal on the dielectric.

5. In a process for the manufacture of electrostatic condensers, thesteps which comprise applying to the weak spots of a dielectric andtheir immediate vicinity, a substance giving of! vapours in vacuo, anddepositing metal on the dielectric in vacuo.

6. In a process for the manufacture of electrostatic condensers, thesteps which comprise applying a hydrocarbon like substance to the weakspots of a dielectric and their immediate vicinity, and depositing metalon the dielectric in vacuo.

7. In a process for the manufacture of electrostatic condensers, thesteps which comprise applying a fat or oil to the weak spots of adielectric and their immediate vicinity, and depositing metal on thedielectric in vacuo.

8. In a process for the manufacture of electrostatic condensers, thesteps which comprise applying to the weak spots of a dielectric andtheir immediate vicinity, a thin coating of a substance giving oflvapours in vacuo, and depositing metal on the dielectric in vacuo.

9. In a process for the manufacture of electrostatic condensers, thesteps which comprise applying to the weak spots of a dielectric andtheir immediate vicinity, a coating of a solid or semisolid substancegiving off vapours in vacuo, and depositing metal on the dielectric invacuo.

10. In a process for the manufacture of electrostatic condensers, thesteps which comprise applying to the back side of a dielectric a liquidor- 11. An electrostatic condenser consisting of a metal coateddielectric, the metal of which is absent from places around the weakspots of the dielectric, the edges of the metal adjacent said weak spotsbeing smooth and unfused.

12. A process for the manufacture of a metallized dielectric forelectrostatic condensers comprising depositing a metal coating on thegreater part'oi a surface of a dielectric while preventing deposit ofmetal on defective portions of said surface.

13. A process for the manufacture of a metallized dielectric forelectrostatic condensers comprising applying a metallization-inhibitingsubstance to the weak spots of a dielectric, and applying a coating ofmetal to the portions of the dielectric not covered by said substance.

14. In a process for the manufacture oi. electrostatic' condensers, thesteps which comprise applying a metal coating to a dielectric andpreventing by mechanical means the application of the metal coating toweak places of the dielectric.

15. In a process for the manufacture of electrostatic condensers, thesteps which comprise applying a metal coating to a dielectric andpreventing by chemical means the application of the metal coating toweak places of the dielectric.

16. In a process for themanufacture of electrostatic condensers, thesteps which comprise applying a metal coating to a dielectric andcovering defective places of the dielectric to prevent application ofmetal to the covered portions of.

